The present invention relates to an electrostatic coater, and typically relates to safety measures when a coater abnormally approaches a workpiece (an object to be coated).
For example, electrostatic coaters are generally used for coating of automobiles. The coating of automobiles has been robotized. A coating robot is installed in a coating booth. The coating booth is an explosion-proof space. The coating robot is connected to a controller installed outside the coating booth via a cable. An electrostatic coater of the coating robot is controlled based on an instruction from the controller.
Patent Literature 1 (Japanese Patent Laid-Open No. 2012-50949) discloses an electrostatic coater in which a high-voltage generator is incorporated. This type of electrostatic coater includes a bleeder resistance for safety measures in addition to the incorporated high-voltage generator, and the electrostatic coater is grounded via the bleeder resistance at all times. When power supply to the electrostatic coater is stopped, a charge accumulated in the electrostatic coater is discharged outside through the bleeder resistance. Accordingly, an accident due to the charge retained in the electrostatic coater immediately after the power supply is stopped would be prevented from occurring. For example, a spark discharge when the electrostatic coater abnormally approaches a workpiece can be prevented from occurring.
Patent Literature 1: Japanese Patent Laid-Open No. 2012-50949
Coating efficiency of electrostatic coating is defined as follows. The coating efficiency means a ratio of an amount of paint attached to the workpiece to an amount of paint discharged toward the workpiece from the electrostatic coater. When the coating efficiency is improved, an amount of paint usage can be reduced, so that various means for improving the coating efficiency have been taken. An example of the means is given in which a voltage applied to the electrostatic coater is increased to a higher voltage. Another example is given in which a distance between the electrostatic coater and the workpiece is decreased.
However, the means for improving the coating efficiency as described above bring a tendency to increase a risk of the occurrence of the spark discharge between the electrostatic coater and the workpiece. Accordingly, a method has been considered as safety measures thereof in which a resistance value of the bleeder resistance is lowered.
The bleeder resistance is incorporated in the electrostatic coater in order to partially discharge power supplied to the electrostatic coater at all times for safety measures. When the resistance value of the bleeder resistance is lowered, an amount of discharged power is increased. That is, lowering the value of the bleeder resistance causes an increase in power amount wastefully discharged outside from the power supplied to the electrostatic coater. This means that an absolute value of a high voltage applied to the electrostatic coater is reduced to cause a decrease in coating quality and a decrease in coating efficiency. Thus, there occurs a problem that a power amount supplied to the electrostatic coater needs to be increased in order to maintain the same absolute value of the high voltage applied to the electrostatic coater as that of a conventional case.
An object of the present invention is to provide an electrostatic coater and an electrostatic coating method capable of neutralizing a charge remaining in the electrostatic coater at an early stage when power supply to the electrostatic coater is stopped.
Another object of the present invention is to provide an electrostatic coater capable of preventing a spark discharge from occurring between the electrostatic coater and a workpiece when a voltage applied to the electrostatic coater is increased and/or when a distance between the electrostatic coater and the workpiece is decreased in order to improve coating efficiency of electrostatic coating.
Yet another object of the present invention is to provide an electrostatic coater having safety measures instead of bleeder resistance when power supply to the electrostatic coater is forcibly stopped based on an electrostatic system that detects a value of a current flowing between the electrostatic coater and a workpiece, and forcibly stops the power supply to the electrostatic coater when the value indicates an abnormal value.